Adiponectin is a kind of adipocytokines excreted from adipocytes, and is indicated to be closely related to metabolic syndrome. To date, in order to improve metabolic syndrome, various substances, including lactic acid (Patent literature 1), yeasts (Patent literature 2), hydrothermal extracts of plant worm (Patent literature 3), triglyceride (Patent literature 4), acylamide compounds (Patent literature 5) and others, have been investigated with the aim of facilitating adiponectin production. Meanwhile, there have been attempts by administering adiponectin or fragments thereof into the body to treat or prevent cancers (Patent literature 6), inflammatory diseases (Patent literature 7), arterial sclerosis (Patent literature 8) and others. Furthermore, adiponectin has been reported to activate AMP kinase in the hypothalamus and to increase food intake (Non-patent literature 1), and an appetite control model by adiponectin has been proposed (Non-patent literature 2).
The inventors of the present invention have already searched for the possibility of oral administration of adiponectin, and investigated the biological activity of adiponectin upon its oral administration (Non-patent literature 3); the contents of this study required further investigation and verification.